Conical Nanochannel Research Articles

Effect of some geometrical characteristics of asymmetric nanochannels on acceleration-driven flow

The geometrical effects of a rough wall asymmetric conical nanochannel on the mass flux of a simple liquid flow are studied via molecular dynamics simulations. Both static and dynamic driving forces are applied to each fluid atom to form a so-called acceleration or force-driven flow. The mean-zero time-dependent periodic dynamic force is applied to induce a net flow as a ratchet. The results show that when the static driving forces are strong enough, there is a symmetry breakdown between mass fluxes in divergent and convergent channels. Thus, by applying a dynamic force, a net mass flux is induced (toward the convergent direction). In this paper, the effects of three different geometrical parameters are investigated. Simulation results indicate that (1) if the radiuses of the two sides of the channel are kept constant, there is a certain length in which the net flux induced by ratchet motion has a maximum value; (2) when the length and the radius of the smaller area of the channel are kept constant, increasing the other side radius generally increases the flux in ratchet motion, and (3) increasing channel length in constant apex angle increases the flux in ratchet motion. The simulation results are justified with molecular principals to provide a better understanding of flow in such nanochannels. The results can be applicable in designing and optimizing nanofluidic devices such as thermocapillary pumps, ion pumps, and Brownian pumps.

A biomimetic multi-stimuli-response ionic gate using a hydroxypyrene derivation-functionalized asymmetric single nanochannel.

A highly efficient multi-stimuli-response ionic gate that can be activated separately or cooperatively by pH and UV light has been demonstrated by modifying the environmental stimuli-responsive molecule 8-hydroxypyrene-1,3,6-trisulfonate into a track-etched single conical nanochannel. Such a multi-response ionic gate can find applications in areas such as electronics, actuators, and biosensors.

Ultratrace detection of glucose with enzyme-functionalized single nanochannels

A sensitive nano-device ford-glucose detection is prepared by modifying a single conical polymer nanochannel with GOx enzymes.

Optofluidic Characterization of Nanoporous Membranes

An optofluidic method that accurately identifies the internal geometry of nanochannel arrays is presented. It is based on the dynamics of capillary-driven fluid imbibition, which is followed by laser interferometry. Conical nanochannel arrays in anodized alumina are investigated, which present an asymmetry of the filling times measured from different sides of the membrane. It is demonstrated by theory and experiments that the capillary filling asymmetry only depends on the ratio H of the inlet to outlet pore radii and that the ratio of filling times vary closely as H(7/3). Besides, the capillary filling of conical channels exhibits striking results in comparison to the corresponding cylindrical channels. Apart from these novel results in nanoscale fluid dynamics, the whole method discussed here serves as a characterization technique for nanoporous membranes.

Malachite Green Derivative–Functionalized Single Nanochannel: Light‐and‐pH Dual‐Driven Ionic Gating

A highly efficient and perfectly reversible ionic gate that can be activated by pH or UV light is demonstrated. Switching between the OFF state and the ON state is mainly dependent on the surface charge transition brought about by a malachite green derivative attached to the interior surface of an ion track-etched conical nanochannel, which makes it suitable for confined spaces. Applications in electronics, actuators, and biosensors can be foreseen.

Selective discrimination of small hydrophobic biomolecules based on ion-current rectification in conically shaped nanochannel

In this study, based on ion-current rectification in the conically shaped nanochannel embedded in polyethylene terephthalate (PET) membrane, we have selectively discriminated three small biomolecules. Because three positive biomolecules (Hoechst 33342, Propidium and Bupivacaine) have different hydrophobicities, their interactions with inside wall of the conical nanochannel are different and their binding affinities can be derived from Langmuir absorption model. Therefore, we can successfully discriminate these small biomolecules. The highest binding constant was obtained for the small molecule with highest hydrophobicity. Another interesting result is that the detection limit for the small molecule with the highest binding constant shifts to submicromole.

Optical Gating of Photosensitive Synthetic Ion Channels

Abstract4‐oxo‐4‐(pyren‐4‐ylmethoxy) butanoic acid is used as a photolabile protecting group to show the optical gating of nanofluidic devices based on synthetic ion channels. The inner surface of the channels is decorated with monolayers of photolabile hydrophobic molecules that can be removed by irradiation, which leads to the generation of hydrophilic groups. This process can be exploited in the UV‐light‐triggered permselective transport of ionic species in aqueous solution through the channels. The optical gating of a single conical nanochannel and multichannel polymeric membranes is characterised experimentally and theoretically by means of current–voltage and selective permeation measurements, respectively. It is anticipated that the integration of nanostructures into multifunctional devices is feasible and can readily find applications in light‐induced controlled release, sensing, and information processing.

PH-Reversed ionic current rectification displayed by conically shaped nanochannel without any modification

Ion current through a nascent nanochannel with conically shaped geometry in PET (polyethylene terephthalate) membrane sandwiched between two same buffer solutions at pH ≤ 3 was routinely considered to exhibit no rectification and, if any, much weaker rectification than that for a nanochannel with a negative surface charge, since the surface charge on the membrane decreases to zero along with decreasing the pH value of the buffer solution down to the pK(a) of carboxylic acid. However, in this study, we discovered that in the buffer solution with low ionic strength at pH values below 3, the conically shaped nanochannels exhibited distinct ion current rectification, as expected for nanochannels with a positive surface charge, if voltages beyond ±2V range were scanned. We reasoned that the current rectification engendered by the positive surface charge of a conical nanochannel was due to further protonation of the hydrogen bonded hydrogel layer or neutral carboxylic acid inside the nanochannel. Therefore, our results enrich the knowledge about nanochannel technology and indicate that a nanofluidic diode based on pH-reversed ion current rectification through a conical nanochannel can be achieved without any modification of the PET membrane.

Sequence-Specific Recognition of DNA Oligomer Using Peptide Nucleic Acid (PNA)-Modified Synthetic Ion Channels: PNA/DNA Hybridization in Nanoconfined Environment

Here we demonstrate the design and construction of a simple, highly sensitive and selective nanofluidic sensing device, based on a single synthetic conical nanochannel for the sequence specific detection of single-stranded DNA oligonucleotides. The biosensing performance of the device depends sensitively on the surface charge and chemical groups incorporated on the inner channel wall that act as binding sites for different analytes. Uncharged peptide nucleic acid (PNA) probes are covalently immobilized on the channel surface through carbodiimide coupling chemistry. This diminishes the channel surface charge, leading to a significant decrease in the rectified ion current flowing through the channel. The PNA-modified channel acts as a highly specific and selective device for the detection of a complementary single-stranded DNA sequence. Upon PNA/DNA hybridization, the channel surface charge density increased due to the presence of the negatively charged DNA strand. The changes in the surface charge-dependent current-voltage (I-V) curves and rectification ratio of the channel confirm the success of immobilization and PNA/DNA hybridization within a confined space at the nanoscale. In addition, a control experiment indicated that the biosensor exhibits remarkable specificity toward a cDNA strand and also has the ability to discriminate single-base mismatch DNA sequences on the basis of rectified ion flux through the nanochannel. In this context, we envision that the single conical nanochannels functionalized with a PNA probe will provide a biosensing platform for the detection and discrimination of short single-stranded DNA oligomer of unknown sequence.